This core will develop highly selective, high affinity antibodies to investigate coordinated cell signaling. Antibodies will be generated to distinguish active forms of target enzymes. The antibodies will be isolated from an established cDNA, single-chain immune library displayed on ribosomes. This library will be screened using modified peptides that mimic the effector regions of key signal proteins or, alternatively, full- length activated proteins. This objective will be fulfilled in two specific aims: 1. To maintain immune libraries, 2. To isolate single-chain antibodies to specific antigens.